Download Novel genetic aspects of Klinefelter`s syndrome

Molecular Human Reproduction, Vol.16, No.6 pp. 386– 395, 2010
Advanced Access publication on March 12, 2010 doi:10.1093/molehr/gaq019
NEW RESEARCH HORIZONS Review
Novel genetic aspects of Klinefelter’s
syndrome
F. Tüttelmann 1,* and J. Gromoll 2
1
Institute of Human Genetics, University of Münster, Vesaliusweg 12-14, D-48149 Münster, Germany 2Centre of Reproductive Medicine and
Andrology, University of Münster, D-48149 Münster, Germany
*Correspondence address. Tel: +49-251-83-55-404; Fax: +49-251-83-56-995; E-mail: [email protected]
Submitted on January 15, 2010; resubmitted on February 24, 2010; accepted on February 25, 2010
abstract: Klinefelter’s syndrome (KS) is the most common chromosome aneuploidy in males, characterized by at least one supernumerary X chromosome. Although extensively studied, the pathophysiology, i.e. the link between the extra X and the phenotype, largely
remains unexplained. The scope of this review is to summarize the progress made in recent years on the role of the supernumerary X
chromosome with respect to its putative influence on the phenotype. In principal, the parental origin of the X chromosome, genedosage effects in conjunction with (possibly skewed) X chromosome inactivation, and—especially concerning spermatogenesis—meiotic
failure may play pivotal roles. One of the X chromosomes is inactivated to achieve dosage-compensation in females and probably likewise
in KS. Genes from the pseudoautosomal regions and an additional 15% of other genes, however, escape X inactivation and are candidates for
putatively constituting the KS phenotype. Examples are the SHOX genes, identified as likely causing the tall stature regularly seen in KS.
Lessons learned from comparisons with normal males and especially females as well as other sex chromosomal aneuploidies are presented.
In addition, genetic topics concerning fertility and counseling are discussed.
Key words: Klinefelter’s syndrome / X chromosome / X inactivation / parental origin / sex chromosome aneuploidy
Introduction
Klinefelter’s syndrome (KS) was first described in 1942 (Klinefelter et al.,
1942), and the cause for the syndrome was later found in 1959 as a
supernumerary X chromosome resulting in the karyotype 47,XXY
(Jacobs and Strong, 1959). About 80–90% of KS cases bear this ‘original’ karyotype,, whereas the remaining exhibit (in decreasing frequency)
varying mosaicism (e.g. 47,XXY/46,XY), carry additional sex chromosomes (48,XXXY; 48,XXYY; 49,XXXXY) or structurally abnormal
X chromosomes (Bojesen et al., 2003; Lanfranco et al., 2004). In the
late 1960s and early 1970s, six large surveys of consecutive newborns
(summarized by Hook and Hamerton, 1977) among other chromosomal aneuploidies established the prevalence of KS as 1 per 1000
same sex births. Later studies found a higher prevalence of up to 1 in
500 boys (Nielsen and Wohlert, 1990), and recently an increase in
the prevalence of KS in opposition to the other sex chromosome trisomies (47,XYY males and 47,XXX females) has been described (Morris
et al., 2008). In any case, KS is the most common chromosomal aberration in men with 0.1–0.2% of the male population affected. When considering infertile men, the prevalence of KS is even much higher and
increases from 3% in unselected to 13% in azoospermic patients
(Van Assche et al., 1996; Vincent et al., 2002) which we recently confirmed in our patient cohort (Tüttelmann et al., 2008; Tüttelmann and
Nieschlag, 2009), making KS the most frequent genetic cause of
azoospermia.
KS is regularly associated with hypergonadotropic hypogonadism
and infertility due to azoospermia, but with marked variations in the
phenotype (Lanfranco et al., 2004). The ‘prototypic’ man with KS
has traditionally been described as tall, with sparse body hair, gynecomastia, small testes and decreased verbal intelligence (Bojesen and
Gravholt, 2007). Yet, the clinical picture of XXY males may range
from severe signs of androgen deficiency, or even a lack of spontaneous puberty, to normally virilised males who only consult a
doctor because of their infertility. This variability is most likely explaining why only 10% of KS men are diagnosed until puberty and only
25% during their lifetime according to a large Danish registry study
(Bojesen et al., 2003) in accordance with an earlier report (Abramsky
and Chapple, 1997).
The increased morbidity and mortality in KS (Bojesen et al., 2004,
2006; Swerdlow et al., 2005) underline the need for an early diagnosis
of a larger proportion of KS and necessitate a more widespread screening. Unchanged, the gold standard for diagnosing KS remains karyotyping of metaphase spreads from cultured peripheral blood lymphocytes.
The major benefit of karyotype analysis is the simultaneous evaluation of
the chromosome structure with respect to translocations, inversions
and deletions. Nevertheless, a suspected diagnosis of KS may be
quickly corroborated by analysis of a buccal smear to detect Barr
bodies (Kamischke et al., 2003), i.e. the inactivated supernumerary
X chromosomes (see below), but does not reach an adequate sensitivity to serve for screening (Pena and Sturzeneker, 2003). In the last
& The Author 2010. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved.
For Permissions, please email: [email protected]
Novel genetic aspects of KS
years, new screening methods have been published: fluorescence in situ
hybridization (FISH) may be used to estimate mosaicism in more detail
by analyzing a larger number of interphase nuclei (Abdelmoula et al.,
2004; Lenz et al., 2005). The extra X can also be detected by quantitative real-time PCR (qPCR) of, for example, the androgen receptor
(AR) gene (Fodor et al., 2007; Ottesen et al., 2007; Plaseski et al.,
2008) or array comparative genomic hybridization (array CGH, Ballif
et al., 2006). In comparison to karyotyping, the benefit of both
methods is the lack of time-consuming and costly cell culture, and
whereas qPCR can be considered a quick and inexpensive method,
the main advantage of array CGH is the higher resolution of up to or
even below 1 kb of altered DNA.
Although KS has been studied extensively in the last decades, the
pathophysiology, i.e. the link between the supernumerary X and the
phenotype, largely remains unclear and the variability unexplained.
Apart from normal interindividual genetic variation, several genetic
mechanisms may explain the variability of the phenotype, clinical features, life circumstances, life expectancy and fertility (Simpson et al.,
2003): in principal, the parental origin of the X chromosome, genedosage effects in conjunction with (possibly skewed) X chromosome
inactivation (XCI) (Samango-Sprouse, 2001), and—especially concerning spermatogenesis—meiotic failure may play pivotal roles.
Much knowledge was and will be gained from the available mouse
models of KS (Lue et al., 2001; Lewejohann et al., 2009), which is
dealt with in detail in a separate paper in this issue (Wistuba, 2010).
The scope of this review is to summarize, from a genetical viewpoint,
the progress made in recent years on the role of the supernumerary X
chromosome with respect to its putative influence on the phenotype.
The human X chromosome,
inactivation and gene-dosage
The human sex chromosomes (X and Y) originate from an ancestral
homologous chromosome pair, which during mammalian evolution
lost homology due to progressive degradation of the Y chromosome
(Charlesworth and Charlesworth, 2005; Graves, 2006). In addition to
specific regions, both sex chromosomes carry short regions of homology termed pseudoautosomal regions (PAR) as they behave like
an autosome and recombine during meiosis (Helena Mangs and
Morris, 2007). As depicted in Fig. 1, while PAR1 comprises 2.6 Mb
of the short-arm tips of both X and Y chromosomes, PAR2 at the
tips of the long arms spans a much shorter region of 320 kb (Freije
et al., 1992; Rappold, 1993). Since the human X chromosome has
been almost completely sequenced, it became clear that (i) PAR1 contains at least 24 genes whereas in PAR2 only 4 genes were identified
and that (ii) probably as many as 10% of X chromosomal genes are
specifically expressed in the testis (Ross et al., 2005).
Following Lyon’s hypothesis (1961), one X chromosome is transcriptionally inactivated in somatic cells of females to equalize the
dosage of X-encoded genes to that of male cells, consequently
leading to cellular mosaicism for X-linked parental alleles. The inactive
X had already been noted by Barr and Bertram (1949), termed Barr
body, which can easily be stained from, for example, a buccal
smear. XCI may occur randomly or by imprinting where the paternal
X chromosome is silenced in the preimplantation embryo and extraembryonic tissue. Random XCI occurs in the epiblast, inactivating
387
Figure 1 Human X chromosome with G-bands (Giemsa stained),
pseudoautosomal regions (PAR1/2) marked to scale and approximate position of exemplary genes described in the text.
SHOX, short stature homeobox; FTHL17, ferritin, heavy polypeptide-like 17; XIST,
X (inactive)-specific transcript (non-protein coding); PGK1, phosphoglycerate kinase
1; PCDH11X, protocadherin 11 X-linked; SYBL1 synaptobrevin-like1 (also: VAMP7
vesicle-associated membrane protein 7)
either the maternally or paternally inherited X chromosome (Ng
et al., 2007), resulting in an active and an inactive chromosome and
this state is then stably transmitted to descendant cells (Kalantry
et al., 2009). The X-inactivation centre initiating XCI contains the X
(inactive) specific transcript (XIST) encoding an untranslated RNA
able to coat and silence the X chromosome. However, besides noncoding transcripts such as XIST, XCI involves chromatin modifiers and
factors of nuclear organization (Chow and Heard, 2009). Together
these lead to a changed chromatin structure and the spatial reorganization of the then silenced X chromosome. XIST itself is regulated by
CpG-sites of the promoter region which, if methylated, repress transcription on the active X chromosome, and are, in contrast, unmethylated and transcriptionally active on the inactive X.
Whereas it is quite obvious that the PARs are not inactivated
to achieve the same gene-dosage in both sexes, things get more
complicated as also single genes and whole regions of the ‘inactive’
X chromosome-specific sections are actually not silenced already in
females (Sudbrak et al., 2001). By evaluating the expression of
X-linked genes, it was found that 30% of the genes on Xp and in contrast ,3% of the genes on Xq may escape inactivation. In total, 5% of
X-linked genes escape inactivation and an additional 10% show a variable pattern of XCI (Carrel et al., 1999; Carrel and Willard, 2005).
388
The KS phenotype may therefore reflect either two active copies of
these strictly X-linked genes or three active copies of X–Y homologous
genes (from the PARs) because of gene-dosage (more active copies
presumably leading to a higher gene expression). Admittedly, for the
former, it is necessary to postulate that somatic cells in 47,XXY
males inactivate the supernumerary X in the same manner as those
in females. This assumption has gained support lately, when Monkhorst
et al. (2008, 2009) showed that XCI is related to the X to autosomal
ratio (which is the same in 47,XXY males as in 46,XX females), at
least in polyploid mouse embryonic stem cells. Additional studies investigating XCI specifically in KS are presented below.
Origin of Klinefelter’s syndrome
In opposition to autosomal trisomies, which only in a minority of
10% are paternally derived, the supernumerary X in half of KS
cases originates from paternal non-disjunction (Thomas and
Hassold, 2003). Although maternal XXY can be caused by nondisjunction during the first and second meiotic divisions or during
early postzygotic mitotic divisions in the developing zygote, XXY of
paternal origin can arise only by meiosis I errors as paternal nondisjunction during meiosis II leads to XXX or XYY zygotes (Fig. 2,
Lanfranco et al., 2004). An association of the frequency of KS with
increasing maternal age at conception has been reported in
Tüttelmann and Gromoll
accordance with other (primarily 13, 18, 21) chromosome trisomies
(Hook, 1981), and a study by Harvey et al. (1990) could attribute
this increase of KS to maternal meiosis I errors. In contrast, an association of paternally derived XXY with the father’s age remains debatable among some confirming studies (Carothers and Filippi, 1988;
Lorda-Sanchez et al., 1992) and some contradictory reports (Jacobs
et al., 1988; Harvey et al., 1990; MacDonald et al., 1994). Evidence
for such an association would come from the finding that sperm aneuploidies increase with age (Eskenazi et al., 2002; Arnedo et al., 2006),
which is, however, also objected by others (Luetjens et al., 2002;
Martin, 2008). The reported increase in KS prevalence over the last
decades was attributable only to paternal origin and hypothesized to
be caused by environmental factors interfering with paternal meiosis I
(Morris et al., 2008). As Herlihy and Halliday (2008) pointed out, a
more obvious reason might well be an overall increasing paternal
age, but this needs to be tested by detailed analyses of larger cohorts.
Pathophysiology and genotype/
phenotype
Rough estimates of the pathophysiology of KS may be derived from
comparing the phenotype associated with the ‘classic’ 47,XXY constitution with other sex chromosome aneuploidies. Among others, the
Figure 2 Different parental origins of KS by non-dysjunction (depicted by flash) in maternal meiosis I (A), maternal meiosis II (B), during one of the
first postzygotic divisions (C) and paternal meiosis I (D).
389
Novel genetic aspects of KS
correlation with the phenotype is more firmly established in higher
order sex chromosome aneuploidies (48,XXXY etc.) than in KS:
the clinical picture progressively deviates from normal as the
number of X chromosomes increases and the frequency of almost
any somatic anomaly is higher compared with 47,XXY (Visootsak
et al., 2001). XXXY and XXXXY males present with characteristic
facial and skeletal malformations, intrauterine growth retardation
and psychomotor retardation (Linden et al., 1995; Simsek et al.,
2009). Another rare, closely related sex chromosomal aneuploidy,
the 48,XXYY syndrome, with a prevalence of 1/18 000 to
1/40 000 displays physiological patterns similar to KS such as tall
stature, hypergonadotropic hypogonadims and infertility, but differently from KS and like the other higher order aneuploidies is associated with significantly more severe neurodevelopmental and
psychological features (Tartaglia et al., 2008). Similar to KS, these
men exhibit a remarkable phenotypic variation which, like in KS,
might be influenced by DNA methylation effects and/or the
(CAG)n repeat polymorphism of the androgen receptor (both discussed later). On the basis of reports of KS patients with X isochromosomes (a chromosome that has lost one of its arms and replaced it
with a copy of the other arm), the long arm of the X chromosome
(Xq) seems to primarily contribute to the KS phenotype (Arps
et al., 1996; Höckner et al., 2008). Interestingly, the phenotype
closely resembles that of 47,XXY KS, but with the important exception of tall stature which thus should be related to Xp.
As described above, in 47,XXY men, the supernumerary
X chromosome is inherited from the mother and the father in
50%, respectively (Thomas and Hassold, 2003), and may affect
the phenotype by differential expression of paternal versus maternal
alleles, i.e. imprinting (Iitsuka et al., 2001). Apart from that, maternal
non-disjunction during meiosis I leads to uniparental heterodisomy
(two different X chromosomes from the same parent, in this case
the mother), while an error during meiosis II results in uniparental
isodisomy (duplicate of one maternal X chromosome in the child). If
the father contributes the extra X, the child will bear two different
X chromosomes of different paternal origin (Fig. 1). To date, six
studies analyzed parental origin with respect to the KS phenotype
with inconsistent results (Table I): four studies investigated a wide
range of features from anthropometric measures (including penile
length and testicular volume), hormones, psychotic symptoms, to cognitive and motor development and did not find any differences
between KS patients carrying a paternal compared with a maternal
extra X (Zinn et al., 2005; Ross et al., 2006, 2008; Zeger et al.,
2008). On the other hand, in their study of 61 KS men, Stemkens
et al. (2006) demonstrated a higher incidence of developmental problems in speech/language (88% versus 59%) and motor impairment
(77% versus 46%) when the supernumerary X chromosome was
paternally inherited. In addition, they found all anthropometric
measures related to body size greater in the paternal X group,
although only head circumference, sitting height and penile length
reached statistical significance. Body height was borderline significantly
higher (P ¼ 0.05). In concordance with an influence of the parental
origin, Wikström et al. (2006) described a later onset of puberty indicated by clinical markers (Tanner stage) and hormone measurements
in the paternal X group, albeit in a small group of 14 boys. This is to
date also the only study analyzing hetero- versus isodisomy and the
authors did not find an influence on the phenotype.
The human androgen receptor (AR, previously also HUMARA,
located in Xq11.2 –q12) is of double interest concerning genotype/
phenotype correlations in KS. The AR contains a highly polymorphic
Table I Summary of studies reporting parental origin of the supernumerary X chromosome, X inactivation, androgen
receptor (AR) (CAG)n repeat length, or combinations associated with KS phenotype.
Study
KS subjects
(n: age)
Outcome measures
Genetic analyses
Results
.............................................................................................................................................................................................
Zitzmann et al. (2004)
77: 18– 65 years
Anthropo- and sociometrical data, X inactivation, AR
features of hypogonadism
(CAG)n
(gynecomastia, etc.), hormones
Zinn et al. (2005)
35: 0.1– 39 years
Anthropometric measurements
including penile length and
testicular volume
Stemkens et al. (2006)
61: 2– 56 years
Anthropometric and psychomotor Paternal origin
development, IQ
Impaired speech and motor development
problems more often in paternal X cases
Ross et al. (2006)
11: 19– 54 years
Psychotic symptoms
No association
Wikström et al. (2006) 14: 10– 13.9 years Pubertal development, growth,
testicular volume, hormones
AR (CAG)n positively correlated with body
height and predictive for gynecomastia and
smaller testes; AR (CAG)n inversely correlated
with bone density, stable partnership and
higher education
Parental origin, X
AR (CAG)n inversely correlated with penile
inactivation, AR (CAG)n length
Parental origin, X
inactivation
Paternal origin of X chromosome associated
Parental origin, iso/
with later onset of puberty; longer AR (CAG)n
hetrodisomy, X
inactivation, AR (CAG)n with later reactivation of pituitary-testicular axis
Ross et al. (2008)
50: 4.1– 17.8 years Cognitive and motor development Parental origin, X
No associations
inactivation, AR (CAG)n
Zeger et al. (2008)
55: 2.0– 14.6
Anthropometric measurements
including penile length and
testicular volume; hormones
Parental origin
No association
390
Tüttelmann and Gromoll
trinucleotide repeat (CAG)n in exon 1 (Choong and Wilson, 1998)
with the normal length varying between 9 and 36/37 repeats
(Zitzmann and Nieschlag, 2003); expanded repeats are associated
with the neurological disorder of X-linked spinobulbar muscular
atrophy (La Spada et al., 1991). The (CAG)n repeat is correlated
with physiological androgen effects in healthy men and probably has
pharmacogenetic implications as well, because testosterone treatment
effects seem to be modulated by its number (reviewed in Zitzmann,
2009). On the contrary, a long sought association of the (CAG)n
with male infertility remains elusive (Davis-Dao et al., 2007; Tüttelmann et al., 2007). Since the AR contains two methylation-sensitive
HpaII restriction sites close to the (CAG)n repeat, a comparison of
PCR products obtained before (both alleles) and after (only inactive,
i.e. methylated allele) digestion can also be used to detect XCI
(Allen et al., 1992). In subjects with two X chromosomes (females
and KS alike), an estimation of the biological activity of the AR is not
as straightforward as in 46,XY males with just one copy, but should
depend on the (CAG)n length corrected for the XCI ratio. Therefore,
the calculation of a so-called ‘X-weighted mean’ taking both into
account has been introduced and correlations with clinical features
have been described (Hickey et al., 2002), including KS (Table I).
We found a positive correlation between (CAG)n length and body
height and an inverse relation with bone density and arm span to
body height ratio in a large study of 77 KS men. In addition, the presence of long (CAG)n had predictive power for having gynecomastia
and smaller testes, whereas short (CAG)n were associated with a
stable partnership and professions requiring higher education; clinical
measures (LH suppression, prostate growth, hemoglobin concentration) under testosterone substitution were also correlated (Zitzmann et al., 2004). Subsequently, Zinn et al. (2005) described an
inverse relationship of (CAG)n and penile length and Wikström
et al. (2006) reported an association of longer (CAG)n with a later
reactivation of the pituitary –gonadal axis in KS boys. On the contrary,
Ross et al. (2008) could not find an influence of (CAG)n length on
cognitive and motor development in a quite large study of 50 KS
boys. The common notion that AR activity is inversely correlated to
(CAG)n repeat length derived from in vitro and in vivo studies has
recently been challenged by a new in vitro study which might possibly
also explain the discrepant findings in vivo (Nenonen et al., 2010).
Assuming a random XCI, the ratio of activation/inactivation at any
X-chromosomal allele outside the PARs would be expected to be
50%. Conversely, while analyzing XCI in KS, a skewed inactivation,
usually defined as above 80% activation/inactivation, of one allele
was detected in a variable percentage of cases. When all studies published so far are reviewed, the percentage of skewed XCI ranges from
below 10 to over 40 (Table II). Furthermore, we found a preferential
inactivation of the shorter allele (Zitzmann et al., 2004), which would
magnify the impact of the (CAG)n length, but this has not been replicated so far. In contrast, Suzuki et al. (2001) found a generally preferred inactivation of the longer allele (but only analyzed seven
men), whereas the two successive studies found no preferential XCI
at all (Zinn et al., 2005; Wikström et al., 2006).
Further studies investigated XCI of other genes than the AR but
essentially remain single reports. Ross et al. (2006) described that in
KS men, PCDH11X/Y is unmethylated (three active copies) and
escapes XCI in contrast to SYBL1. Both genes are expressed in the
brain and were hypothesized to play a role in the cognitive phenotype
of KS. PCDH11X/Y is located in the human XY non-PAR homology
region in Xq21.3 and SYBL1 in PAR2 (Helena Mangs and Morris,
2007; Wilson et al., 2007). By using a whole-genome expression
array, Vawter et al. (2007) found differential expression of 129
genes comparing 11 KS and 6 XY males with X-chromosomal genes
being overrepresented (14 of 129). The authors also describe correlations of the differentially expressed genes with measures of verbal
cognition, but the sample size is probably too small to draw definite
conclusions. In a different approach using pyrosequencing, Chung
et al. (2006) investigate inactivation of X-chromosomal genes. They
identified 14 genes escaping XCI, of which 7 show a profile
Table II Summary of studies analyzing X inactivation in KS patients.
Study
Subjects (n)
Locus analyzed
X inactivation*
.............................................................................................................................................................................................
Iitsuka et al. (2001)
14 KS
AR (CAG)n
21% (3) skewed
Suzuki et al. (2001)
7 KS
AR (CAG)n
43% (3) skewed, longer allele preferred overall
Zitzmann et al. (2004)
46 KS
AR (CAG)n
11% (5) skewed, shorter allele preferred
Zinn et al. (2005)
22 KS
AR (CAG)n
9% (2) skewed, no preferential allele
Wikström et al. (2006)
6 KS
AR (CAG)n
33% (2) skewed, no preferential allele
Ross et al. (2008)
26 KS
AR (CAG)n
8% (2) skewed
Ross et al. (2006)
11 KS
SYBL1**
2 methylated, 1 unmethylated, comparable to
females
PCDH11X/Y**
All 3 unmethylated (escapes inactivation)
Chung et al. (2006)
5 KS, 5 XX
14 genes
7 escape inactivation, comparable to females; other
7 genes without clear result
Poplinski et al. (2010)
10 KS, XY, XX each
XIST, PGK1
50% methylated as in females
SHOX
Low, comparable to females
FTHL17
High, comparable to females
*.80% methylation, skewed inactivation.
**Gene from the pseudoautosomal region, three gene copies in KS patients.
391
Novel genetic aspects of KS
comparable to females, whereas the results of the other 7 genes did
not suffice for definite conclusions. Recently, we could furthermore
demonstrate a comparable XIST promoter methylation of 50% in KS
comparable with that in females. Low methylation (below 10%) of
SHOX (from PAR1), 50% methylation PGK1 (indicator of XCI)
and high methylation (above 90%) of FTHL17 were also similar in
47,XXY and 46,XX (Poplinski et al., 2010).
Summarizing, the role of the AR (CAG)n repeat polymorphism has
been studied quite extensively in KS boys and men, but without reaching a uniform picture. Neither the number of repeats nor the XCI
pattern is uniformly associated with aspects of the KS phenotype,
which might primarily be due to the wide range of features under
investigation (e.g. psychological and anthropometric measures, hormones), but also in part to the heterogeneous study protocols of
highly variable sample sizes and age groups. Whether XCI is skewed
more often in KS than in females or the noted percentages of
skewed XCI are just the extremes of a Gaussian distribution
remains to be determined. In addition, the question arises whether
aging affects (skewed) XCI in KS as has been postulated in women
(Sharp et al., 2000) which is currently a topic of intensive debate
(Swierczek et al., 2008; Busque et al., 2009). Overall, the collected
data, albeit sparse and regularly limited to single studies, support
that (i) XCI in KS follows the same pattern as in females and (ii) therefore XCI escapees in females probably also escape inactivation in KS,
then possibly being overexpressed and involved in the phenotype.
Further knowledge may be gained by comparing KS with other sex
chromosomal aneuploidies, especially 45,X (Turner’s syndrome)
females and 46,XX males. Turner’s syndrome is characterized by a
completely or in part missing second X chromosome and approximately affects 1 in 2000–2500 live female births (Nielsen and
Wohlert, 1990; Stochholm et al., 2006). Over 90% of patients
exhibit the common features of short stature and premature ovarian
failure (Bondy, 2009). The XX male syndrome on the other hand is
rare, occurring approximately in 1 in 20 000 newborn males. The phenotype had not been well defined, but was recently described in detail
from our collection of 11 affected men (Vorona et al., 2007). In agreement with others (Aksglaede et al., 2008), we found 46,XX males to
be of significantly shorter stature than healthy as well as KS men while
otherwise quite similar to KS. Concerning the KS phenotype, both
entities are interesting with respect to the explanation of increased
body height in XXY. Short stature in Turner’s syndrome is caused
by haploinsufficiency for the pseudoautosomal gene SHOX encoding
a transcription factor expressed in the developing skeleton and implicated in various skeletal anomalies seen in 45,X. Consistent with these
data, 46,XX males reach a mean body height lower than control males
but comparable to healthy females. The SHOX gene’s role in short
stature is firmly established starting from Turner syndrome expanding
to idiopathic short stature (Ellison et al., 1997; Rao et al., 1997;
Blaschke and Rappold, 2006). Fittingly, SHOX is overall nonmethylated in 46,XX males and females (Poplinski et al., 2010), and
the abnormal growth patterns cannot be explained by different
serum levels of IGF-I and IGFBP-3 (exerting growth hormone
effects). Furthermore, KS boys exhibit an accelerated growth already
from an age of 6 years onward, when an effect of sex hormones is
highly unlikely (Aksglaede et al., 2008). An effect of SHOX overdosage
was reported by several authors in females with varying supernumerary X chromosome constitutions (Adamson et al., 2002;
Kanaka-Gantenbein et al., 2004; Alvarez-Vazquez et al., 2006;
Nishi et al., 2008). Consequently, the tall stature in KS may not be
mainly due to hypogonadism as previously thought, i.e. lower testosterone/estrodial levels not stopping long-bone growth by inducing epiphysial growth plate fusion. On the contrary, increased body height
may well be caused by excessive expression of growth-related genes
with SHOX as the leading candidate as 47,XXY carry three copies.
Therefore, SHOX can be considered an example of a gene-dosage
effect of a pseudoautosomal gene in KS.
Another example arises from investigations of autoimmune disease,
which usually show a marked predominance in women. For systemic
lupus erythematosus (SLE), Scofield et al. (2008) recently described
a high prevalence of KS of 1 in 43 men in their cohort of male SLE
patients equaling an 14-fold increase in comparison to the population frequency. Consequently, the risk for SLE in KS men is comparable to that in 46,XX females and 14-fold higher than in 46,XY men.
Interestingly, only one of these five men had been diagnosed with KS
before. Moreover, an underrepresentation of females with Turner’s
syndrome may exist, but cannot be reliably determined from the
data available. Hence, an involvement of gene-dosage effects and/or
XCI in the pathogenesis of SLE and probably other autoimmune
diseases is likely (Selmi, 2008; Sawalha et al., 2009).
Fertility
The X chromosome exhibits genes (99 out of 1098) specifically
expressed in the testis (Ross et al., 2005). Thus, it is not surprising
that also the fertility status of XXY patients is affected and highly variable (Aksglaede et al., 2006). With the advent of microdissection
(microsurgical) testicular sperm extraction, the chances to retrieve
spermatozoa in KS patients are reported to range between 30% and
70% (Schiff et al., 2005; Koga et al., 2007; Yarali et al., 2009) and
the possibility for KS men to become fathers utilizing in vitro fertilization with intracytoplasmatic sperm injection (ICSI) arises. Concurrently, the main question of how spermatogenesis is disturbed in KS
or, put the other way around, how it still works, becomes of increasing
importance with respect to the risk for the offspring of, for example,
chromosomal aneuploidy. The degeneration of germ cells in KS may in
principal be caused by the supernumerary X itself preventing the completion of meiosis, or, on the other hand, a disturbed testicular
environment involving somatic Sertoli and Leydig cells (Aksglaede
et al., 2006), which currently remains unresolved. On the contrary,
recent findings may shed light on the long debated question
whether 47,XXY spermatogonia are able to complete meiosis or, in
contrast, some spermatogonia lose the supernumerary X chromosome becoming normal 46,XY cells and then proceed through
meiosis. While others previously postulated the completion of
meiosis of 47,XXY spermatogonia supported by indirect clues
(Foresta et al., 1999), Sciurano et al. (2009) nicely showed by FISH
analyses that all meiotic spermatocytes were euploid 46,XY. In
addition, the frequency of sperm sex chromosome aneuploidies
would be expected to be as high as 50% if 47,XXY spermatogonia
were meiotically competent, while this recent work further fits an at
most slightly elevated risk in KS men (reviewed in Hall et al., 2006;
Martin, 2008). Concordantly, the outcome of children of KS fathers
is overall reassuring, albeit a minor, but significant, increase of incidence of KS boys and, surprisingly, also of autosomal aberrations
392
has been reported (Staessen et al., 2003). Because the analyzed
number of pregnancies from KS fathers is still low with around 200
cases, all of which, of course, achieved by ICSI which in itself bears
a slightly higher risk for chromosomal aberrations, final conclusions
cannot be drawn.
A topic gaining interest is fertility preservation by cryopreservation
of immature testicular tissue in prepubertal boys undergoing gonadotoxic therapies because of malignant disease. This would also be an
interesting option for KS patients, since degeneration of seminiferous
tubules in KS seems to accelerate with puberty (Wikström and
Dunkel, 2008). Testicular biopsies obtained earlier and then permanently stored (established) could be used to derive gametes for fertilization in the future by in vitro maturation (including meiosis), which at
present, however, remains entirely experimental (Wyns et al., 2010).
The prerequisite for such a procedure would be the earlier diagnosis
of KS boys, though, which could be achieved by introducing the new
and inexpensive screening methods like qPCR (presented earlier).
One miscellaneous issue concerning KS and fertility is the analysis of
microdeletions of the Y chromosome, i.e. AZF (azoospermia factor)
deletions. Mitra et al. (2006) reported a surprisingly high incidence
of AZFa and AZFb deletions in 4 out of 14 KS patients, which was
not confirmed by screening of large numbers (.200) of KS patients
from our patient cohort (Simoni et al., 2008) and others (Choe
et al., 2007). Nevertheless, another study was carried out with an
amazingly high percentage of six out of nine KS patients supposed
to bear an AZF deletion (Hadjkacem-Loukil et al., 2009). Both
studies reporting this high microdeletion prevalence have to be questioned because the deletions presented were rather unconventional,
mostly involving only isolated markers of the AZFa, AZFb and/or
AZFc regions. Since these deletions were not confirmed with an
independent method such as Southern blotting, they should probably
be regarded as methodological artifacts. Indeed, based on the much
larger cohorts of patients, it was confirmed that deletions of the
Y chromosome do not occur in patients with KS.
Genetic counseling
With respect to KS, genetic counseling is necessary in the situations of
a prenatal diagnosis of KS and for couples planning ICSI as in all cases
of male-factor infertility. Considering the high variability of the phenotype, in a large proportion with a benign clinical picture not even diagnosed throughout life, a rate of 70% induced abortion after prenatal
diagnosis of KS (Bojesen et al., 2003; Hamamy and Dahoun, 2004)
seems high. Meschede et al. (1998) reported a markedly lower rate
of pregnancy termination which may depend on cultural differences
in parental perception of sex chromosomal polysomies but probably
also on characteristics of genetic counseling at our institution.
Health professionals providing genetic counseling influence the
parents’ decision against or toward pregnancy termination with the
pregnancy more likely to continue if the counseling is given by a
specialized geneticist (Hall et al., 2001; Marteau et al., 2002). When
ICSI is planned, the genetic risks resulting from this procedure
should be discussed with each couple. The above-mentioned, probably slightly increased risks for autosomal as well as sex chromosomal
aberrations arising by the 47,XXY constitution of the father and to
some extent implicated through ICSI itself need to be discussed.
The potential benefits and risks of preimplantation or prenatal
Tüttelmann and Gromoll
diagnosis (by chorionic villous sampling or amniocentesis) genetic diagnosis should be considered depending on the technical and legal availability. Summing up, genetic counseling is recommended in all cases of
a new diagnosis of KS whether pre- or post-natally and in any case of
couples undergoing ICSI.
Conclusions
The frequency and variability of KS make it the most common as well
as heavily underdiagnosed chromosome aneuploidy in men. The currently available knowledge provides hints to the pathophysiology and
genotype/phenotype correlations of the supernumerary X chromosome. Gene-dosage effects, of which SHOX related to the tall
stature in KS is a leading example, in combination with (escapees
from) XCI, are most likely constituting the phenotype. Lessons can
also be learned from comparisons with normal males and especially
females as well as other sex chromosomal aneuploidies. The recently
described higher incidence of autoimmune diseases in KS implicates a
need to intensify screening also in these patient groups and not only
focus on male infertility and the ‘classic’ phenotype.
Acknowledgements
The authors thank W. Kramer (University Clinics Münster) for help
with the illustrations.
Funding
This work was established in the framework of the Clinical Research
Award IZKF CRA03/09 of the Medical Faculty Münster.
References
Abdelmoula NB, Amouri A, Portnoi MF, Saad A, Boudawara T, Mhiri MN,
Bahloul A, Rebai T. Cytogenetics and fluorescence in situ hybridization
assessment of sex-chromosome mosaicism in Klinefelter’s syndrome.
Ann Genet 2004;47:163 – 175.
Abramsky L, Chapple J. 47,XXY (Klinefelter syndrome) and 47,XYY:
estimated rates of and indication for postnatal diagnosis with
implications for prenatal counselling. Prenat Diagn 1997;17:363 – 368.
Adamson KA, Cross I, Batch JA, Rappold GA, Glass IA, Ball SG. Trisomy
of the short stature homeobox-containing gene (SHOX), resulting from
a duplication-deletion of the X chromosome. Clin Endocrinol (Oxf) 2002;
56:671 – 675.
Aksglaede L, Wikstrom AM, Rajpert-De Meyts E, Dunkel L,
Skakkebaek NE, Juul A. Natural history of seminiferous tubule
degeneration in Klinefelter syndrome. Hum Reprod Update 2006;
12:39 – 48.
Aksglaede L, Skakkebaek NE, Juul A. Abnormal sex chromosome
constitution and longitudinal growth: serum levels of insulin-like
growth factor (IGF)-I, IGF binding protein-3, luteinizing hormone, and
testosterone in 109 males with 47,XXY, 47,XYY, or sex-determining
region of the Y chromosome (SRY)-positive 46,XX karyotypes. J Clin
Endocrinol Metab 2008;93:169 – 176.
Allen RC, Zoghbi HY, Moseley AB, Rosenblatt HM, Belmont JW.
Methylation of HpaII and HhaI sites near the polymorphic CAG
repeat in the human androgen-receptor gene correlates with X
chromosome inactivation. Am J Hum Genet 1992;51:1229 –1239.
Novel genetic aspects of KS
Alvarez-Vazquez P, Rivera A, Figueroa I, Paramo C, Garcia-Mayor RV.
Acromegaloidism with normal growth hormone secretion associated
with X-tetrasomy. Pituitary 2006;9:145 – 149.
Arnedo N, Templado C, Sanchez-Blanque Y, Rajmil O, Nogues C. Sperm
aneuploidy in fathers of Klinefelter’s syndrome offspring assessed by
multicolour fluorescent in situ hybridization using probes for
chromosomes 6, 13, 18, 21, 22, X and Y. Hum Reprod 2006;21:
524–528.
Arps S, Koske-Westphal T, Meinecke P, Meschede D, Nieschlag E,
Harprecht W, Steuber E, Back E, Wolff G, Kerber S et al.
Isochromosome Xq in Klinefelter syndrome: report of 7 new cases.
Am J Med Genet 1996;64:580 – 582.
Ballif BC, Kashork CD, Saleki R, Rorem E, Sundin K, Bejjani BA, Shaffer LG.
Detecting sex chromosome anomalies and common triploidies in
products of conception by array-based comparative genomic
hybridization. Prenat Diagn 2006;26:333 – 339.
Barr ML, Bertram EG. A morphological distinction between neurones of
the male and female, and the behaviour of the nucleolar satellite
during accelerated nucleoprotein synthesis. Nature 1949;163:676.
Blaschke RJ, Rappold G. The pseudoautosomal regions, SHOX and
disease. Curr Opin Genet Dev 2006;16:233 – 239.
Bojesen A, Gravholt CH. Klinefelter syndrome in clinical practice. Nat Clin
Pract Urol 2007;4:192 – 204.
Bojesen A, Juul S, Gravholt CH. Prenatal and postnatal prevalence of
Klinefelter syndrome: a national registry study. J Clin Endocrinol Metab
2003;88:622 – 626.
Bojesen A, Juul S, Birkebaek N, Gravholt CH. Increased mortality in
Klinefelter syndrome. J Clin Endocrinol Metab 2004;89:3830 – 3834.
Bojesen A, Juul S, Birkebaek NH, Gravholt CH. Morbidity in Klinefelter
syndrome: a Danish register study based on hospital discharge
diagnoses. J Clin Endocrinol Metab 2006;91:1254 – 1260.
Bondy CA. Turner syndrome 2008. Horm Res 2009;71(Suppl. 1):52 – 56.
Busque L, Paquette Y, Provost S, Roy DC, Levine RL, Mollica L, Gilliland DG.
Skewing of X-inactivation ratios in blood cells of aging women is
confirmed by independent methodologies. Blood 2009;113:
3472 – 3474.
Carothers AD, Filippi G. Klinefelter’s syndrome in Sardinia and Scotland.
Comparative studies of parental age and other aetiological factors in
47,XXY. Hum Genet 1988;81:71 – 75.
Carrel L, Willard HF. X-inactivation profile reveals extensive variability in
X-linked gene expression in females. Nature 2005;434:400 – 404.
Carrel L, Cottle AA, Goglin KC, Willard HF. A first-generation
X-inactivation profile of the human X chromosome. Proc Natl Acad Sci
USA 1999;96:14440 – 14444.
Charlesworth D, Charlesworth B. Sex chromosomes: evolution of the
weird and wonderful. Curr Biol 2005;15:R129– R131.
Choe JH, Kim JW, Lee JS, Seo JT. Routine screening for classical
azoospermia factor deletions of the Y chromosome in azoospermic
patients with Klinefelter syndrome. Asian J Androl 2007;9:815 – 820.
Choong CS, Wilson EM. Trinucleotide repeats in the human androgen
receptor: a molecular basis for disease. J Mol Endocrinol 1998;21:235–257.
Chow J, Heard E. X inactivation and the complexities of silencing a sex
chromosome. Curr Opin Cell Biol 2009;21:359 – 366.
Chung IH, Lee HC, Park JH, Ko JJ, Lee SH, Chung TG, Kim HJ, Cha KY,
Lee S. The biallelic expression pattern of X-linked genes in Klinefelter
syndrome by pyrosequencing. Am J Med Genet A 2006;140:527 – 532.
Davis-Dao CA, Tuazon ED, Sokol RZ, Cortessis VK. Male infertility and
variation in CAG repeat length in the androgen receptor gene: a
meta-analysis. J Clin Endocrinol Metab 2007;92:4319– 4326.
Ellison JW, Wardak Z, Young MF, Gehron Robey P, Laig-Webster M,
Chiong W. PHOG, a candidate gene for involvement in the short
stature of Turner syndrome. Hum Mol Genet 1997;6:1341 – 1347.
393
Eskenazi B, Wyrobek AJ, Kidd SA, Lowe X, Moore D II, Weisiger K,
Aylstock M. Sperm aneuploidy in fathers of children with paternally
and maternally inherited Klinefelter syndrome. Hum Reprod 2002;
17:576– 583.
Fodor F, Kamory E, Csokay B, Kopa Z, Kiss A, Lantos I, Tisza T. Rapid
detection of sex chromosomal aneuploidies by QF-PCR: application in
200 men with severe oligozoospermia or azoospermia. Genet Test
2007;11:139 – 145.
Foresta C, Galeazzi C, Bettella A, Marin P, Rossato M, Garolla A, Ferlin A.
Analysis of meiosis in intratesticular germ cells from subjects affected by
classic Klinefelter’s syndrome. J Clin Endocrinol Metab 1999;
84:3807– 3810.
Freije D, Helms C, Watson MS, Donis-Keller H. Identification of a second
pseudoautosomal region near the Xq and Yq telomeres. Science 1992;
258:1784– 1787.
Graves JA. Sex chromosome specialization and degeneration in mammals.
Cell 2006;124:901 – 914.
Hadjkacem-Loukil L, Ghorbel M, Bahloul A, Ayadi H, Ammar-Keskes L.
Genetic association between AZF region polymorphism and
Klinefelter syndrome. Reprod Biomed Online 2009;19:547 – 551.
Hall S, Marteau TM, Limbert C, Reid M, Feijoo M, Soares M, Nippert I,
Bobrow M, Cameron A, Van Diem M et al. Counselling following the
prenatal diagnosis of Klinefelter syndrome: comparisons between
geneticists and obstetricians in five European countries. Community
Genet 2001;4:233 – 238.
Hall H, Hunt P, Hassold T. Meiosis and sex chromosome aneuploidy: how
meiotic errors cause aneuploidy; how aneuploidy causes meiotic errors.
Curr Opin Genet Dev 2006;16:323 – 329.
Hamamy HA, Dahoun S. Parental decisions following the prenatal
diagnosis of sex chromosome abnormalities. Eur J Obstet Gynecol
Reprod Biol 2004;116:58 – 62.
Harvey J, Jacobs PA, Hassold T, Pettay D. The parental origin of 47,XXY
males. Birth Defects Orig Artic Ser 1990;26:289 – 296.
Helena Mangs A, Morris BJ. The human pseudoautosomal region (PAR):
origin, function and future. Curr Genomics 2007;8:129– 136.
Herlihy AS, Halliday J. Is paternal age playing a role in the changing
prevalence of Klinefelter syndrome? Eur J Hum Genet 2008;
16:1173– 1174, author reply 1174.
Hickey T, Chandy A, Norman RJ. The androgen receptor CAG repeat
polymorphism and X-chromosome inactivation in Australian
Caucasian women with infertility related to polycystic ovary
syndrome. J Clin Endocrinol Metab 2002;87:161– 165.
Höckner M, Pinggera GM, Gunther B, Sergi C, Fauth C, Erdel M, Kotzot D.
Unravelling the parental origin and mechanism of formation of the
47,XY,i(X)(q10) Klinefelter karyotype variant. Fertil Steril 2008;
90:2009.e13– 2009.e17.
Hook EB. Rates of chromosome abnormalities at different maternal ages.
Obstet Gynecol 1981;58:282– 285.
Hook EB, Hamerton JL. The frequency of chromosome abnormalities
detected in consecutive newborn studies—differences between
studies, results by sex and severity of phenotypic involvement. In:
Porter IH, Hook EB (eds). Population Cytogenetics. New York:
National Academy Press, 1977, 63 –79.
Iitsuka Y, Bock A, Nguyen DD, Samango-Sprouse CA, Simpson JL,
Bischoff FZ. Evidence of skewed X-chromosome inactivation in 47,XXY
and 48,XXYY Klinefelter patients. Am J Med Genet 2001;98:25– 31.
Jacobs PA, Strong JA. A case of human intersexuality having a possible
XXY sex-determining mechanism. Nature 1959;183:302 – 303.
Jacobs PA, Hassold TJ, Whittington E, Butler G, Collyer S, Keston M,
Lee M. Klinefelter’s syndrome: an analysis of the origin of the
additional sex chromosome using molecular probes. Ann Hum Genet
1988;52:93 – 109.
394
Kalantry S, Purushothaman S, Bowen RB, Starmer J, Magnuson T. Evidence
of Xist RNA-independent initiation of mouse imprinted X-chromosome
inactivation. Nature 2009;460:647 – 651.
Kamischke A, Baumgardt A, Horst J, Nieschlag E. Clinical and diagnostic
features of patients with suspected Klinefelter syndrome. J Androl
2003;24:41 – 48.
Kanaka-Gantenbein C, Kitsiou S, Mavrou A, Stamoyannou L, Kolialexi A,
Kekou K, Liakopoulou M, Chrousos G. Tall stature, insulin resistance,
and disturbed behavior in a girl with the triple X syndrome harboring
three SHOX genes: offspring of a father with mosaic Klinefelter
syndrome but with two maternal X chromosomes. Horm Res 2004;
61:205 – 210.
Klinefelter HF, Reifenstein EC, Albright F. Syndrome characterized by
gynecomastia, aspermatogenesis without Leydigism, increased
excretion of follicle stimulating hormone. J Clin Endocrinol 1942;
2:615 – 627.
Koga M, Tsujimura A, Takeyama M, Kiuchi H, Takao T, Miyagawa Y,
Takada S, Matsumiya K, Fujioka H, Okamoto Y et al. Clinical
comparison of successful and failed microdissection testicular sperm
extraction in patients with nonmosaic Klinefelter syndrome. Urology
2007;70:341 – 345.
La Spada AR, Wilson EM, Lubahn DB, Harding AE, Fischbeck KH.
Androgen receptor gene mutations in X-linked spinal and bulbar
muscular atrophy. Nature 1991;352:77 – 79.
Lanfranco F, Kamischke A, Zitzmann M, Nieschlag E. Klinefelter’s
syndrome. Lancet 2004;364:273– 283.
Lenz P, Luetjens CM, Kamischke A, Kuhnert B, Kennerknecht I,
Nieschlag E. Mosaic status in lymphocytes of infertile men with or
without Klinefelter syndrome. Hum Reprod 2005;20:1248– 1255.
Lewejohann L, Damm OS, Luetjens CM, Hamalainen T, Simoni M,
Nieschlag E, Gromoll J, Wistuba J. Impaired recognition memory in
male mice with a supernumerary X chromosome. Physiol Behav 2009;
96:23 – 29.
Linden MG, Bender BG, Robinson A. Sex chromosome tetrasomy and
pentasomy. Pediatrics 1995;96:672 – 682.
Lorda-Sanchez I, Binkert F, Maechler M, Robinson WP, Schinzel AA.
Reduced recombination and paternal age effect in Klinefelter
syndrome. Hum Genet 1992;89:524 – 530.
Lue Y, Rao PN, Sinha Hikim AP, Im M, Salameh WA, Yen PH, Wang C,
Swerdloff RS. XXY male mice: an experimental model for Klinefelter
syndrome. Endocrinology 2001;142:1461 – 1470.
Luetjens CM, Rolf C, Gassner P, Werny JE, Nieschlag E. Sperm aneuploidy
rates in younger and older men. Hum Reprod 2002;17:1826 –1832.
Lyon MF. Gene action in the X-chromosome of the mouse (Mus musculus
L.). Nature 1961;190:372 – 373.
MacDonald M, Hassold T, Harvey J, Wang LH, Morton NE, Jacobs P. The
origin of 47,XXY and 47,XXX aneuploidy: heterogeneous mechanisms
and role of aberrant recombination. Hum Mol Genet 1994;
3:1365 – 1371.
Marteau TM, Nippert I, Hall S, Limbert C, Reid M, Bobrow M,
Cameron A, Cornel M, van Diem M, Eiben B et al. Outcomes of
pregnancies diagnosed with Klinefelter syndrome: the possible
influence of health professionals. Prenat Diagn 2002;22:562 – 566.
Martin RH. Meiotic errors in human oogenesis and spermatogenesis.
Reprod Biomed Online 2008;16:523 – 531.
Meschede D, Louwen F, Nippert I, Holzgreve W, Miny P, Horst J. Low
rates of pregnancy termination for prenatally diagnosed Klinefelter
syndrome and other sex chromosome polysomies. Am J Med Genet
1998;80:330 – 334.
Mitra A, Dada R, Kumar R, Gupta NP, Kucheria K, Gupta SK. Y
chromosome microdeletions in azoospermic patients with Klinefelter’s
syndrome. Asian J Androl 2006;8:81 – 88.
Tüttelmann and Gromoll
Monkhorst K, Jonkers I, Rentmeester E, Grosveld F, Gribnau J. X
inactivation counting and choice is a stochastic process: evidence for
involvement of an X-linked activator. Cell 2008;132:410 – 421.
Monkhorst K, de Hoon B, Jonkers I, Mulugeta Achame E, Monkhorst W,
Hoogerbrugge J, Rentmeester E, Westerhoff HV, Grosveld F,
Grootegoed JA et al. The probability to initiate X chromosome
inactivation is determined by the X to autosomal ratio and X
chromosome specific allelic properties. PLoS One 2009;4:e5616.
Morris JK, Alberman E, Scott C, Jacobs P. Is the prevalence of Klinefelter
syndrome increasing? Eur J Hum Genet 2008;16:163 – 170.
Nenonen H, Bjork C, Skjaerpe PA, Giwercman A, Rylander L, Svartberg J,
Giwercman YL. CAG repeat number is not inversely associated
with androgen receptor activity in vitro. Mol Hum Reprod 2010;16:
153 – 157.
Ng K, Pullirsch D, Leeb M, Wutz A. Xist and the order of silencing. EMBO
Rep 2007;8:34 –39.
Nielsen J, Wohlert M. Sex chromosome abnormalities found among
34,910 newborn children: results from a 13-year incidence study in
Arhus, Denmark. Birth Defects Orig Artic Ser 1990;26:209 – 223.
Nishi MY, Correa RV, Costa EM, Billerbeck AE, Cruzes AL, Domenice S,
Carvalho LR, Mendonca BB. Tall stature and poor breast development
after estrogen replacement in a hypergonadotrophic hypogonadic
patient with a 45,X/46,X,der(X) karyotype with SHOX gene
overdosage. Arq Bras Endocrinol Metabol 2008;52:1282 –1287.
Ottesen AM, Garn ID, Aksglaede L, Juul A, Rajpert-De Meyts E. A simple
screening method for detection of Klinefelter syndrome and other
X-chromosome aneuploidies based on copy number of the androgen
receptor gene. Mol Hum Reprod 2007;13:745 – 750.
Pena SD, Sturzeneker R. Molecular barr bodies: methylation-specific PCR
of the human X-linked gene FMR-1 for diagnosis of Klinefelter
syndrome. J Androl 2003;24:809, author reply 810.
Plaseski T, Noveski P, Trivodalieva S, Efremov GD, Plaseska-Karanfilska D.
Quantitative fluorescent-PCR detection of sex chromosome
aneuploidies and AZF deletions/duplications. Genet Test 2008;
12:595 – 605.
Poplinski A, Wieacker P, Kliesch S, Gromoll J. Severe XIST
hypomethylation clearly distinguishes (SRY+) 46,XX-maleness from
Klinefelter syndrome. Eur J Endocrinol 2010;162:169 – 175.
Rao E, Weiss B, Fukami M, Rump A, Niesler B, Mertz A, Muroya K,
Binder G, Kirsch S, Winkelmann M et al. Pseudoautosomal deletions
encompassing a novel homeobox gene cause growth failure in
idiopathic short stature and Turner syndrome. Nat Genet 1997;
16:54 – 63.
Rappold GA. The pseudoautosomal regions of the human sex
chromosomes. Hum Genet 1993;92:315 – 324.
Ross MT, Grafham DV, Coffey AJ, Scherer S, McLay K, Muzny D,
Platzer M, Howell GR, Burrows C, Bird CP et al. The DNA sequence
of the human X chromosome. Nature 2005;434:325– 337.
Ross NL, Wadekar R, Lopes A, Dagnall A, Close J, Delisi LE, Crow TJ.
Methylation of two Homo sapiens-specific X – Y homologous genes in
Klinefelter’s syndrome (XXY). Am J Med Genet B Neuropsychiatr Genet
2006;141B:544 – 548.
Ross JL, Roeltgen DP, Stefanatos G, Benecke R, Zeger MP, Kushner H,
Ramos P, Elder FF, Zinn AR. Cognitive and motor development
during childhood in boys with Klinefelter syndrome. Am J Med Genet A
2008;146A:708 –719.
Samango-Sprouse C. Mental development in polysomy X Klinefelter
syndrome (47,XXY; 48,XXXY): effects of incomplete X inactivation.
Semin Reprod Med 2001;19:193 – 202.
Sawalha AH, Harley JB, Scofield RH. Autoimmunity and Klinefelter’s
syndrome: when men have two X chromosomes. J Autoimmun 2009;
33:31 – 34.
Novel genetic aspects of KS
Schiff JD, Palermo GD, Veeck LL, Goldstein M, Rosenwaks Z, Schlegel PN.
Success of testicular sperm extraction [corrected] and intracytoplasmic
sperm injection in men with Klinefelter syndrome. J Clin Endocrinol Metab
2005;90:6263 – 6267.
Sciurano RB, Luna Hisano CV, Rahn MI, Brugo Olmedo S, Rey
Valzacchi G, Coco R, Solari AJ. Focal spermatogenesis originates in
euploid germ cells in classical Klinefelter patients. Hum Reprod 2009;
24:2353– 2360.
Scofield RH, Bruner GR, Namjou B, Kimberly RP, Ramsey-Goldman R,
Petri M, Reveille JD, Alarcon GS, Vila LM, Reid J et al. Klinefelter’s
syndrome (47,XXY) in male systemic lupus erythematosus patients:
support for the notion of a gene-dose effect from the X
chromosome. Arthritis Rheum 2008;58:2511 –2517.
Selmi C. The X in sex: how autoimmune diseases revolve around sex
chromosomes. Best Pract Res Clin Rheumatol 2008;22:913 – 922.
Sharp A, Robinson D, Jacobs P. Age- and tissue-specific variation of X
chromosome inactivation ratios in normal women. Hum Genet 2000;
107:343– 349.
Simoni M, Tüttelmann F, Gromoll J, Nieschlag E. Clinical consequences of
microdeletions of the Y chromosome: the extended Münster
experience. Reprod Biomed Online 2008;16:289 – 303.
Simpson JL, de la Cruz F, Swerdloff RS, Samango-Sprouse C,
Skakkebaek NE, Graham JM Jr, Hassold T, Aylstock M,
Meyer-Bahlburg HF, Willard HF et al. Klinefelter syndrome: expanding
the phenotype and identifying new research directions. Genet Med
2003;5:460 – 468.
Simsek PO, Utine GE, Alikasifoglu A, Alanay Y, Boduroglu K, Kandemir N.
Rare sex chromosome aneuploidies: 49,XXXXY and 48,XXXY
syndromes. Turk J Pediatr 2009;51:294 – 297.
Staessen C, Tournaye H, Van Assche E, Michiels A, Van Landuyt L,
Devroey P, Liebaers I, Van Steirteghem A. PGD in 47,XXY
Klinefelter’s syndrome patients. Hum Reprod Update 2003;9:319 – 330.
Stemkens D, Roza T, Verrij L, Swaab H, van Werkhoven MK, Alizadeh BZ,
Sinke RJ, Giltay JC. Is there an influence of X-chromosomal imprinting
on the phenotype in Klinefelter syndrome? A clinical and molecular
genetic study of 61 cases. Clin Genet 2006;70:43– 48.
Stochholm K, Juul S, Juel K, Naeraa RW, Gravholt CH. Prevalence,
incidence, diagnostic delay, and mortality in Turner syndrome. J Clin
Endocrinol Metab 2006;91:3897 – 3902.
Sudbrak R, Wieczorek G, Nuber UA, Mann W, Kirchner R, Erdogan F,
Brown CJ, Wohrle D, Sterk P, Kalscheuer VM et al. X
chromosome-specific cDNA arrays: identification of genes that escape
from X-inactivation and other applications. Hum Mol Genet 2001;
10:77– 83.
Suzuki Y, Sasagawa I, Tateno T, Ashida J, Nakada T, Muroya K, Ogata T.
Mutation screening and CAG repeat length analysis of the androgen
receptor gene in Klinefelter’s syndrome patients with and without
spermatogenesis. Hum Reprod 2001;16:1653– 1656.
Swerdlow AJ, Higgins CD, Schoemaker MJ, Wright AF, Jacobs PA, United
Kingdom Clinical Cytogenetics Group. Mortality in patients with
Klinefelter syndrome in Britain: a cohort study. J Clin Endocrinol Metab
2005;90:6516 – 6522.
Swierczek SI, Agarwal N, Nussenzveig RH, Rothstein G, Wilson A, Artz A,
Prchal JT. Hematopoiesis is not clonal in healthy elderly women. Blood
2008;112:3186 – 3193.
Tartaglia N, Davis S, Hench A, Nimishakavi S, Beauregard R, Reynolds A,
Fenton L, Albrecht L, Ross J, Visootsak J et al. A new look at XXYY
syndrome: medical and psychological features. Am J Med Genet A
2008;146A:1509 –1522.
Thomas NS, Hassold TJ. Aberrant recombination and the origin of
Klinefelter syndrome. Hum Reprod Update 2003;9:309 –317.
395
Tüttelmann F, Nieschlag E. Classification of andrological disorders. In:
Nieschlag E, Behre HM, Nieschlag S (eds). Andrology: Male
Reproductive Health and Dysfunction. Springer: Heidelberg, 2009, 87 – 92.
Tüttelmann F, Rajpert-De Meyts E, Nieschlag E, Simoni M. Gene
polymorphisms and male infertility—a meta-analysis and literature
review. Reprod Biomed Online 2007;15:643 – 658.
Tüttelmann F, Gromoll J, Kliesch S. Genetics of male infertility. Urologe A
2008;47:1561 – 1567.
Van Assche E, Bonduelle M, Tournaye H, Joris H, Verheyen G, Devroey P,
Van Steirteghem A, Liebaers I. Cytogenetics of infertile men. Hum
Reprod 1996;11(Suppl. 4):1– 24.
Vawter MP, Harvey PD, DeLisi LE. Dysregulation of X-linked gene
expression in Klinefelter’s syndrome and association with verbal
cognition. Am J Med Genet B Neuropsychiatr Genet 2007;144B:
728 – 734.
Vincent MC, Daudin M, De Mas P, Massat G, Mieusset R, Pontonnier F,
Calvas P, Bujan L, Bourrouillout G. Cytogenetic investigations of
infertile men with low sperm counts: a 25-year experience. J Androl
2002;23:18 – 22, discussion 44 – 45.
Visootsak J, Aylstock M, Graham JM Jr. Klinefelter syndrome and its
variants: an update and review for the primary pediatrician. Clin
Pediatr (Phila) 2001;40:639 – 651.
Vorona E, Zitzmann M, Gromoll J, Schüring AN, Nieschlag E. Clinical,
endocrinological, and epigenetic features of the 46,XX male
syndrome, compared with 47,XXY Klinefelter patients. J Clin
Endocrinol Metab 2007;92:3458 – 3465.
Wikström AM, Dunkel L. Testicular function in Klinefelter syndrome.
Horm Res 2008;69:317 – 326.
Wikström AM, Painter JN, Raivio T, Aittomaki K, Dunkel L. Genetic
features of the X chromosome affect pubertal development and
testicular degeneration in adolescent boys with Klinefelter syndrome.
Clin Endocrinol (Oxf) 2006;65:92 – 97.
Wilson ND, Ross LJ, Close J, Mott R, Crow TJ, Volpi EV. Replication
profile of PCDH11X and PCDH11Y, a gene pair located in the nonpseudoautosomal homologous region Xq21.3/Yp11.2. Chromosome
Res 2007;15:485– 498.
Wistuba J. Animal models for Klinefelter’s syndrome and their relevance
for the clinic. Mol Hum Reprod 2010 (in press).
Wyns C, Curaba M, Vanabelle B, Van Langendonckt A, Donnez J. Options
for fertility preservation in prepubertal boys. Hum Reprod Update 2010;
Epub ahead of Print January 4, 2010.
Yarali H, Polat M, Bozdag G, Gunel M, Alpas I, Esinler I, Dogan U, Tiras B.
TESE-ICSI in patients with non-mosaic Klinefelter syndrome: a
comparative study. Reprod Biomed Online 2009;18:756 – 760.
Zeger MP, Zinn AR, Lahlou N, Ramos P, Kowal K, Samango-Sprouse C,
Ross JL. Effect of ascertainment and genetic features on the
phenotype of Klinefelter syndrome. J Pediatr 2008;152:716 – 722.
Zinn AR, Ramos P, Elder FF, Kowal K, Samango-Sprouse C, Ross JL.
Androgen receptor CAGn repeat length influences phenotype of 47,XXY
(Klinefelter) syndrome. J Clin Endocrinol Metab 2005;90:5041 – 5046.
Zitzmann M. The role of the CAG repeat androgen receptor
polymorphism in andrology. Front Horm Res 2009;37:52– 61.
Zitzmann M, Nieschlag E. The CAG repeat polymorphism within the
androgen receptor gene and maleness. Int J Androl 2003;26:76 – 83.
Zitzmann M, Depenbusch M, Gromoll J, Nieschlag E. X-chromosome
inactivation patterns and androgen receptor functionality influence
phenotype and social characteristics as well as pharmacogenetics of
testosterone therapy in Klinefelter patients. J Clin Endocrinol Metab
2004;89:6208 – 6217.
Zitzmann M, Gromoll J, Nieschlag E. The androgen receptor CAG repeat
polymorphism. Andrologia 2005;37:216.